Fuel cell with protruded gas diffusion layer

ABSTRACT

An assembling operation of a fuel cell is effectively simplified. With the simple and economical structure, the desired sealing function is achieved. The fuel cell ( 10 ) includes a membrane electrode assembly ( 14 ) and first and second metal separators ( 16, 18 ) sandwiching the membrane electrode assembly ( 14 ). Connection channels ( 28   a,    28   b ) are provided on the first metal separator ( 16 ). The connection channels ( 28   a,    28   b ) connect the oxygen-containing gas supply passage ( 20   a ) and the oxygen-containing gas discharge passage ( 20   b ) to the oxygen-containing gas flow field ( 26 ). The membrane electrode assembly ( 14 ) has first overlapping portions ( 66   a,    66   b ) overlapped on the connection channels ( 28   a,    28   b ) for sealing the connection channels ( 28   a,    28   b ). The first overlapping portions ( 66   a,    66   b ) comprise, in effect, a gas diffusion layer.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/558,229 filed 22 Nov. 2005, which is a 35 U.S.C. 371 national stagefiling of International Application No. PCT/JP2004/006971, filed 21 May2004, which claims priority to Japanese Patent Application No.2003-146288 filed 23 May 2003 in Japan. The contents of theaforementioned applications are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to an internal manifold type fuel cellformed by stacking an electrolyte electrode assembly and separators in astacking direction. The electrolyte electrode assembly includes a pairof electrodes and an electrolyte interposed between the electrodes.Reactant gas flow fields for supplying reactant gases along surfaces ofthe electrodes are formed between the electrolyte electrode assembly andthe separators. Reactant gas passages are connected to the reactant gasflow fields, and extending through the fuel cell in the stackingdirection.

BACKGROUND ART

For example, a solid polymer fuel cell includes an electrolyte electrodeassembly (membrane electrode assembly), and separators sandwiching theelectrolyte electrode assembly. The electrolyte electrode assemblyincludes an anode, a cathode, and an electrolyte membrane interposedbetween the anode and the cathode. The electrolyte membrane is a polymerion exchange membrane. In this type of the fuel cell, in use,predetermined numbers of the electrolyte electrode assemblies and theseparators are stacked together to form a fuel cell stack.

In the fuel cell, a fuel gas such as a gas chiefly containing hydrogen(hereinafter also referred to as the “hydrogen-containing gas”) issupplied to the anode. The catalyst of the anode induces a chemicalreaction of the fuel gas to split the hydrogen molecule into hydrogenions and electrons. The hydrogen ions move toward the cathode throughthe electrolyte, and the electrons flow through an external circuit tothe cathode, creating a DC electrical energy. A gas chiefly containingoxygen or air (hereinafter also referred to as the “oxygen-containinggas”) is supplied to the cathode. At the cathode, the hydrogen ions fromthe anode combine with the electrons and oxygen to produce water.

In the fuel cell, a fuel gas flow field (reactant gas flow field) isprovided in a surface of the separator facing the anode for allowing thefuel gas (reactant gas) to flow along the separator, and anoxygen-containing gas flow field (reactant gas flow field) is providedin a surface of the separator facing the cathode for allowing theoxygen-containing gas (reactant gas) to flow along the surface of theseparator. Further, a fuel gas supply passage and a fuel gas dischargepassage as reactant gas passages connected to the fuel gas flow field,and an oxygen-containing gas supply passage and an oxygen-containing gasdischarge passage as reactant gas passages connected to theoxygen-containing gas flow field are provided in the marginal region ofthe separators. The reactant gas passages extend through the separatorsin the stacking direction.

In this case, the reactant gas flow field is connected to the reactantgas passages through connection channels having parallel grooves or thelike for allowing the reactant gases to flow smoothly and uniformly.However, when the separators and the membrane electrode assembly aretightened together such that seal members are interposed between theseparators and the membrane electrode assembly, the seal members may bepositioned inside the connection channels, and the desired sealingperformance cannot be maintained. Further, the reactant gases do notflow suitably.

In an attempt to address the problem, in a solid polymer fuel cell stackdisclosed in Japanese Laid-Open Patent Publication No. 2001-266911, asshown in FIG. 13, a reactant gas flow field such as an oxygen-containinggas flow field 2 in a serpentine pattern is formed in a surface of aseparator 1. The oxygen-containing gas flow field 2 is connected to anoxygen-containing gas supply through hole 3 and an oxygen-containing gasdischarge through hole 4 extending through marginal regions of theseparator 1 in the stacking direction. A packing 5 is provided at theseparator 1. The packing 5 allows the oxygen-containing gas to flowbetween the through holes 3 and 4 and the oxygen-containing gas flowfield 2, while sealing the other through holes to prevent the leakage.

SUS (Stainless steel) plates 7 as seal members are provided at theconnection channels 6 a, 6 b connecting the through holes 3, 4 and theoxygen-containing gas flow field 2 to cover the connection channels 6 a,6 b. Each of the SUS plates 7 has a rectangular shape, and includes ears7 a, 7 b at two positions. The ears 7 a, 7 b are fitted to steps 8formed on the separator 1.

As described above, according to the disclosure of Japanese Laid-OpenPatent Publication No. 2001-266911, the SUS plates 7 as the seal memberscover the connection channels 6 a, 6 b. Therefore, the polymer membrane(not shown) and the packing 5 do not fall into the oxygen-containing gasflow field 2, and the desired sealing performance is achieved. It ispossible to prevent the increase in the pressure loss of the reactantgas.

However, in Japanese Laid-Open Patent Publication No. 2001-266911, theSUS plates 7 are attached to the respective connection channels 6 a, 6 bof the separator 1, and the operation of attaching the SUS plates 7 islaborious. In particular, in the case where several tens to severalhundreds of fuel cells are stacked together, the attachment operation ofthe SUS plates 7 is significantly laborious, and time consuming. Thecost for the operation is very large.

Further, since the SUS plates 7 are attached to the connection channels6 a, 6 b to cover the connection channels 6 a, 6 b, the size of theconnection channels 6 a, 6 b cannot be smaller than the width of the SUSplates 7. Thus, it is difficult to achieve reduction in the overall sizeand weight of the fuel cell.

-   Patent Document 1: Japanese Laid-Open Patent Publication No.    2001-266911

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present invention solves these types of problems, and an object ofthe present invention is to provide a fuel cell which makes it possibleto effectively simplify the assembling operation of the fuel cell, andto achieve the desired sealing function with the economical and simplestructure.

Means for Solving the Problems

In the present invention, a fuel cell is formed by stacking anelectrolyte electrode assembly and separators in a stacking direction.The electrolyte electrode assembly includes a pair of electrodes and anelectrolyte interposed between the electrodes. Reactant gas flow fieldsfor supplying reactant gases along surfaces of the electrodes are formedbetween the electrolyte electrode assembly and the separators. Reactantgas passages are connected to the reactant gas flow fields, andextending through the fuel cell in the stacking direction. A connectionchannel connecting the reactant gas passage and the reactant gas flowfield is provided on the separator, and at least one gas diffusion layerof the electrolyte electrode assembly has an overlapping portionoverlapped on the connection channel such that the overlapping portionis tightly attached on the separator for sealing the connection channel.

Advantageous Effects of the Invention

Therefore, since the gas diffusion layer itself covers the connectionchannel, no dedicated metal plates such as SUS plates are required.Thus, the operation of attaching the metal plates or the like iseliminated. The assembling operation of the fuel cell is simplifiedsignificantly. With the economical and simple structure, it is possibleto achieve the desired sealing function. Further, it is possible tominimize the size of the connection channel, and to achieve reduction inthe overall size and the weight of the fuel cell easily.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an exploded perspective view showing main components of a fuelcell according to a first embodiment of the present invention.

FIG. 2 is a cross sectional view showing a fuel cell stack, taken alonga line II-II in FIG. 1.

FIG. 3 is a cross sectional view showing the fuel cell stack, takenalong a line III-III in FIG. 1.

FIG. 4 is a front view showing a first metal separator of the fuel cell.

FIG. 5 is a front view showing a second metal separator of the fuelcell.

FIG. 6 is an exploded perspective view showing main components of a fuelcell according to a second embodiment of the present invention.

FIG. 7 is a cross sectional view showing a fuel cell stack, taken alonga line VII-VII in FIG. 6.

FIG. 8 is a front view showing a first metal separator of the fuel cell.

FIG. 9 is a front view showing a second metal separator of the fuelcell.

FIG. 10 is an exploded perspective view showing main components of afuel cell according to a third embodiment of the present invention.

FIG. 11 is a front view showing a second metal separator of the fuelcell.

FIG. 12 is a cross sectional view showing part of the fuel cell stack.

FIG. 13 is a front view showing a separator of a conventional fuel cellstack.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is an exploded perspective view showing main components of a fuelcell 10 according to a first embodiment of the present invention. FIG. 2is a cross sectional view showing a fuel cell stack 12 formed bystacking a plurality of the fuel cells 10 in a direction indicated by anarrow A, taken along a line II-II in FIG. 1. FIG. 3 is a cross sectionalview showing the fuel cell stack 12, taken along a line III-III in FIG.1.

As shown in FIG. 1, the fuel cell 10 is formed by sandwiching a membraneelectrode assembly (electrolyte electrode assembly) 14 between first andsecond metal separators 16, 18. For example, the first and second metalseparators 16, 18 are steel plates, stainless steel plates, aluminumplates, or plated steel sheets. Instead of using the first and secondmetal separators 16, 18, for example, carbon separators may be used.

At one end of the fuel cell 10 in a horizontal direction indicated by anarrow B in FIG. 1, an oxygen-containing gas supply passage 20 a forsupplying an oxygen-containing containing gas or the like, a coolantdischarge passage 22 b for discharging a coolant, and a fuel gasdischarge passage 24 b for discharging a fuel gas such as a hydrogencontaining gas are arranged vertically in a direction indicated by anarrow C. The oxygen-containing gas supply passage 20 a, the coolantdischarge passage 22 b, and the fuel gas discharge passage 24 b extendthrough the fuel cell 10 in the stacking direction indicated by thearrow A.

At the other end of the fuel cell 10 in the direction indicated by thearrow B, a fuel gas supply passage 24 a for supplying the fuel gas, acoolant supply passage 22 a for supplying the coolant, and theoxygen-containing gas discharge passage 20 b for discharging theoxygen-containing gas are arranged in the direction indicated by thearrow C. The fuel gas supply passage 24 a, the coolant supply passage 22a, and the oxygen-containing gas discharge passage 20 b extend throughthe fuel cell 10 in the direction indicated by the arrow A.

As shown in FIGS. 1 and 4, the first metal separator 16 has anoxygen-containing gas flow field (reactant gas flow field) 26 on asurface 16 a facing the membrane electrode assembly 14. Theoxygen-containing gas flow field 26 has a serpentine pattern includingtwo turn regions and three straight regions for allowing theoxygen-containing gas to flow back and forth in the direction indicatedby the arrow B. The oxygen-containing gas flow field 26 comprises aplurality of grooves formed by corrugating the first metal separator 16.The oxygen-containing gas flow field 26 is connected to theoxygen-containing gas supply passage 20 a and the oxygen-containing gasdischarge passage 20 b through connection channels 28 a, 28 b. Theconnection channels 28 a, 28 b comprise a plurality of parallel flowgrooves divided by a plurality of protrusions 30 a, 30 b extending fromthe oxygen-containing gas flow field 26.

A first seal member 32 is formed integrally on the surfaces 16 a, 16 bof the first metal separator 16, e.g., by heat treatment, injectionmolding or the like, around the outer end of the first metal separator16. The first seal member 32 is made of seal material, cushion materialor packing material such as EPDM (Ethylene Propylene Diene Monomer), NBR(Nitrile Butadiene Rubber), fluoro rubber, silicone rubber, fluorosilicone rubber, butyl rubber, natural rubber, styrene rubber,chloroprene rubber, or acrylic rubber.

The first seal member 32 includes a first planar portion 34 formedintegrally on the surface 16 a of the first metal separator 16, and asecond planar portion 36 formed integrally on the surface 16 b of thefirst metal separator 16. As shown in FIG. 4, the first planar portion34 is formed around the oxygen-containing gas supply passage 20 a, theoxygen-containing gas discharge passage 20 b, and the oxygen-containinggas flow field 26, and allows the oxygen-containing gas to flow from theoxygen-containing gas supply passage 20 a to the oxygen-containing flowfield 26, and flow from the oxygen-containing gas flow field 26 to theoxygen-containing gas discharge passage 20 b. The second planar portion36 allows the coolant to flow from the coolant supply passage 22 a tothe coolant discharge passage 22 b.

The first planar portion 34 includes two short ridges 37 a near theoxygen-containing gas supply passage 20 a, and two short ridges 37 bnear the oxygen-containing gas discharge passage 20 b. Further, twoshort ridges 38 a are formed near the fuel gas supply passage 24 a, andtwo short ridges 38 b are provided near the fuel gas discharge passage24 b.

As shown in FIGS. 1 and 5, the second metal separator 18 has a fuel gasflow field (reactant gas flow field) 40 on a surface 18 a facing themembrane electrode assembly 14. The fuel gas flow field 40 is connectedto the fuel gas supply passage 24 a and the fuel gas discharge passage24 b. The fuel gas flow field 40 has a serpentine pattern including twoturn regions and three straight regions for allowing the fuel gas toflow back and forth in the direction indicated by the arrow B.

The fuel gas flow field 40 comprises a plurality of grooves. The fuelgas flow field 40 is connected to the fuel gas supply passage 24 a andthe fuel gas discharge passage 24 b through connection channels 42 a, 42b. The connection channels 42 a, 42 b comprise a plurality of parallelflow grooves divided by a plurality of protrusions 44 a, 44 b extendingfrom the fuel gas flow field 40.

As shown in FIG. 1, the second metal separator 18 has a coolant flowfield 46 on a surface 18 a opposite to the surface 18 b. The coolantflow field 46 is connected between the coolant supply passage 22 a andthe coolant discharge passage 22 b.

A second seal member 48 is formed integrally on the surfaces 18 a, 18 bof the second metal separator 18 around the outer end of the secondmetal separator 18. The material of the second seal member 48 is thesame as the material of the first seal member 32. As shown in FIG. 5,the second seal member 48 includes a ridge 50 on the surface 18 a of thesecond metal separator 18. The ridge 50 is formed around the fuel gasflow field 40, and allows the fuel gas to flow from the fuel gas supplypassage 24 a to the fuel gas flow field 40, and flow from the fuel gasflow field 40 to the fuel gas discharge passage 24 b.

On the surface 18 a, two short ridges 52 a are formed near the fuel gassupply passage 24 a, and two short ridges 52 b are formed near the fuelgas discharge passage 24 b. Further, two short ridges 54 a are formednear the oxygen-containing gas supply passage 20 a, and two short ridges54 b are formed near the oxygen-containing gas discharge passage 20 b.When the first metal separator 16 and the second metal separator 18 arestacked together, the short ridges 37 a, 37 b and the short ridges 54 a,54 b tightly contact each other (see FIG. 2), and the short ridges 38 a,38 b and the short ridges 52 a, 52 b tightly contact each other.

As shown in FIG. 1, on the surface 18 b, the second seal member 48includes a ridge 56 around the coolant flow field 46. The coolant flowfield 46 allows the coolant to flow from the coolant supply passage 22 ato the coolant flow field 46, and flow from the coolant flow field 46 tothe coolant discharge passage 22 b.

The membrane electrode assembly 14 includes an anode 62, a cathode 64,and a solid polymer electrolyte membrane 60 interposed between the anode62 and the cathode 64. The solid polymer electrolyte membrane 60 isformed by impregnating a thin membrane of perfluorosulfonic acid withwater, for example. The outer marginal portion of the solid polymerelectrolyte membrane 60 protrudes outwardly from the outer marginalportions of the anode 62 and the cathode 64. Each of the anode 62 andthe cathode 64 has a gas diffusion layer such as a carbon paper, and anelectrode catalyst layer of platinum alloy supported on porous carbonparticles. The carbon particles are deposited uniformly on the surfaceof the gas diffusion layer. The electrode catalyst layer of the anode 62and the electrode catalyst layer of the cathode 64 are fixed to bothsurfaces of the solid polymer electrolyte membrane 60, respectively.

As shown in FIGS. 1, 4, and 5, the membrane electrode assembly 14includes first overlapping portions 66 a, 66 b overlapped on theconnection channels 28 a, 28 b of the first metal separator 16 forsealing the connection channels 28 a, 28 b, and second overlappingportions 68 a, 68 b overlapped on the connection channels 42 a, 42 b ofthe second metal separator 18 for sealing the connection channels 42 a,42 b.

As shown in FIGS. 1 and 2, the first overlapping portion 66 a has aprotruded end 64 a protruding from the end of the cathode 64 toward theconnection channel 28 a (outwardly in the direction indicated by thearrow B) in parallel to the surface of the cathode 64. The protruded end64 a is supported by the ridge 50 of the second seal member 48 of thesecond metal separator 18 such that the solid polymer electrolytemembrane 60 is interposed between the protruded end 64 a and the ridge50.

Likewise, the first overlapping portion 66 b has a protruded end 64 bprotruding from the end of the cathode 64 toward the connection channel28 b in parallel to the surface of the cathode 64. The protruded end 64b is supported by the ridge 50 of the second seal member 48 such thatthe solid polymer electrolyte membrane 60 is interposed between theprotruded end 64 b and the ridge 50. The protruded ends 64 a, 64 b areprovided symmetrically at the gas diffusion layer of the cathode 64.

The protruded ends 64 a, 64 b tightly contact the protrusions 30 a, 30 bof the first metal separator 16 for sealing the connection channels 28a, 28 b each comprising a plurality of flow grooves. Theoxygen-containing gas supply passage 20 a and the oxygen-containing gasdischarge passage 20 b are connected to the oxygen-containing gas flowfield 26 through the connection channels 28 a, 28 b.

The second overlapping portions 68 a, 68 b have protruded ends 62 a, 62b protruding from the ends of the anode 62 toward the connectionchannels 42 a, 42 b of the second metal separator 18 in parallel to thesurface of the anode 62. The protruded ends 62 a, 62 b tightly contactthe protrusions 44 a, 44 b of the second metal separator. The protrudedends 62 a, 62 b are provided symmetrically at the gas diffusion layer ofthe anode 62.

The protruded ends 62 a, 62 b seal the connection channels 42 a, 42 b.The fuel gas supply passage 24 a and the fuel gas discharge passage 24 bare connected to the fuel gas flow field 40 through the connectionchannels 42 a, 42 b.

Operation of the fuel cell 10 as having the above structure will bedescribed below.

Firstly, as shown in FIG. 1, a fuel gas such as a hydrogen-containinggas is supplied to the fuel gas supply passage 24 a, and anoxygen-containing gas or the like is supplied to the oxygen-containinggas supply passage 20 a. Further, and a coolant such as pure water,ethylene glycol, or oil is supplied to the coolant supply passage 22 a.

Thus, as shown in FIG. 5, the fuel gas flows from the fuel gas supplypassage 24 a to the fuel gas flow field 40 of the second metal separator18, and flows back and forth in the direction indicated by the arrow B.The fuel gas is supplied to the anode 62 of the membrane electrodeassembly 14. As shown in FIGS. 1 and 4, the oxygen-containing gas flowsfrom the oxygen-containing gas supply passage 20 a to theoxygen-containing gas flow field 26 of the first metal separator 16, andflows back and forth in the direction indicated by the arrow B. Theoxygen-containing gas is supplied to the cathode 64 of the membraneelectrode assembly 14.

Thus, in the membrane electrode assembly 14, the oxygen-containing gassupplied to the cathode 64, and the fuel gas supplied to the anode 62are consumed in the electrochemical reactions at catalyst layers of thecathode 64 and the anode 62 for generating electricity.

Then, the fuel gas supplied to, and consumed at the anode 62 isdischarged through the fuel gas discharge passage 24 b in the directionindicated by the arrow A. Likewise, the oxygen-containing gas suppliedto, and consumed at the cathode 64 is discharged through theoxygen-containing gas discharge passage 20 b in the direction indicatedby the arrow A.

Further, the coolant supplied to the coolant supply passage 22 a flowsinto the coolant flow field 46 between the first and second metalseparators 16, 18, and flows in the direction indicated by the arrow B.After the coolant cools the membrane electrode assembly 14, the coolantis discharged through the coolant discharge passage 22 b.

In the first embodiment, the first overlapping portions 66 a, 66 b andthe second overlapping portions 68 a, 68 b are provided at, at least,part of the membrane electrode assembly 14. The first overlappingportions 66 a, 66 b are overlapped on the connection channels 28 a, 28 bof the first metal separator 16 for sealing the connection channels 28a, 28 b. The second overlapping portions 68 a, 68 b are overlapped onthe connection channels 42 a, 42 b of the second metal separator 18 forsealing the connection channels 42 a, 42 b.

Thus, as shown in FIG. 2, at the first overlapping portion 66 a, thesolid polymer electrolyte membrane 60 tightly contacts the ridge 50 ofthe second seal member 48, and the protruded end 64 a which is, ineffect, the gas diffusion layer tightly contacts the protrusions 30 a ofthe first metal separator 16. The oxygen-containing gas supplied to theoxygen-containing gas supply passage 20 a flows toward the connectionchannel 28 a along the short ridges 37 a, 54 a which tightly contacteach other. Then, the oxygen-containing gas flows smoothly between theprotrusions 30 a in the oxygen-containing gas flow field 26. Thus, it ispossible to effectively prevent the leakage of the oxygen-containinggas.

Therefore, no dedicated metal plate such as the conventional SUS plateis not required for covering the connection channel 28 a. The operationof attaching the metal plate is eliminated. Thus, the assemblingoperation of the fuel cell 10 is simplified significantly. With theeconomical and simple structure, it is possible to achieve the desiredsealing function.

Further, it is possible to minimize the size of the connection channel28 a, and to achieve reduction in the overall size and the weight of thefuel cell 10. Also in the connection channels 28 b, 42 a, 42 b, the sameadvantages as in the case of the connection channel 28 a can beobtained.

FIG. 6 is an exploded perspective view showing main components of a fuelcell 80 according to a second embodiment of the present invention. FIG.7 is a cross sectional view showing a fuel cell stack 82 formed bystacking a plurality of the fuel cells 80 in the direction indicated bythe arrow A, taken along a line VII-VII in FIG. 6. The constituentelements that are identical to those of the fuel cell 10 according tothe first embodiment are labeled with the same reference numeral, anddescription thereof will be omitted. In a third embodiment as describedlater, the constituent elements that are identical to those of the fuelcell 10 according to the first embodiment are labeled with the samereference numeral, and description thereof will be omitted.

The fuel cell 80 includes a membrane electrode assembly (electrolyteelectrode assembly) 84 sandwiched between first and second metalseparators 86, 88. As shown in FIGS. 6 and 8, the oxygen-containing gasflow field 26 is connected to the oxygen-containing gas supply passage20 a and the oxygen-containing gas discharge passage 20 b throughconnection channels 90 a, 90 b. The connection channels 90 a, 90 bcomprise a plurality of parallel flow grooves divided by a plurality ofprotrusions 92 a, 92 b provided separately from protrusions 30 a, 30 bextending from the oxygen-containing gas flow field 26.

As shown in FIG. 9, in the second metal separator 88, the fuel gas flowfield 40 is connected to the fuel gas supply passage 24 a and the fuelgas discharge passage 24 b through the connection channels 94 a, 94 b.The connection channels 94 a, 94 b comprise a plurality of parallel flowgrooves divided by a plurality of protrusions 96 a, 96 b providedseparately from protrusions 44 a, 44 b extending from the fuel gas flowfield 40.

As shown in FIG. 6, a hardened portion 98 formed by impregnation ofadhesive such as fluorinated adhesive is provided at each of theprotruded ends 62 a, 62 b, 64 a, and 64 b. Therefore, when the membraneelectrode assembly 84 is sandwiched between the first and secondseparators 86, 88, the protruded ends 62 a, 62 b, 64 a, and 64 b are notfatigued.

Thus, in the second embodiment, the gas diffusion layer is notpositioned in the connection channels 90 a, 90 b, 94 a, and 94 b, andthe desired sealing performance can be maintained. Further, in thesecond embodiment, the same advantages as in the case of the firstembodiment can be obtained.

FIG. 10 is an exploded perspective view showing main components of afuel cell 120 according to a third embodiment of the present invention.FIG. 11 is a front view showing a second metal separator 122 of the fuelcell 120.

The fuel cell 120 has a membrane electrode assembly 124 including ananode 126, a cathode 64, and a solid polymer electrolyte membrane 60interposed between the anode 126 and the cathode 64. The size of theanode 126 is smaller than the size of the cathode 64.

The second metal separator 122 does not have any connection channels.The second metal separator 122 has a plurality of passages 128 a, 128 bon a surface 122 b where the coolant flow field 46 is provided. Thepassages 128 a, 128 b are connected to the fuel gas supply passage 24 aand the fuel gas discharge passage 24 b, respectively. Also, thepassages 128 a, 128 b are connected to a plurality of holes 130 a, 130b, respectively. The holes 130 a, 130 b are connected to the fuel gasflow field 40 on a surface 122 a.

A second seal member 132 is formed integrally on the surfaces 122 a, 122b of the second metal separator 122. As shown in FIG. 11, the secondseal member 132 includes an outer seal 134 provided on the surface 122 anear the outer end of the second metal separator 122, and an inner seal136 spaced inwardly from the outer seal 134 at a predetermined distance.The inner seal 136 seals the fuel gas flow field 40.

The second seal member 132 includes an outer seal 138 provided on thesurface 122 b of the second metal separator 122, and an inner seal 140spaced inwardly from the outer seal 138 around the coolant flow field 46(see FIGS. 10 and 12).

In the third embodiment having the above structure, the connectionchannels 28 a, 28 b of the first metal separator 16 are sealed by thetwo corners of the cathode 64 (which is, in effect, the gas diffusionlayer) of the membrane electrode assembly 124. Therefore, the sameadvantages as in the cases of the first and second embodiments can beobtained.

INDUSTRIAL APPLICABILITY

In the fuel cell according to the present invention, the gas diffusionlayer of the electrolyte electrode assembly itself covers the connectionchannel. Therefore, no dedicated metal plate or the like is required.Thus, the operation of attaching the metal plate or the like iseliminated. The assembling operation of the fuel cell is simplifiedsignificantly. With the simple and economical structure, the desiredsealing performance can be achieved. Further, the size of the connectionchannel is reduced as much as possible. It is possible to achievereduction in the size and the weight of the fuel cell easily.

1. An internal manifold type fuel cell formed by stacking an electrolyteelectrode assembly and separators in a stacking direction, saidelectrolyte electrode assembly including a pair of electrodes and anelectrolyte membrane interposed between said electrodes, reactant gasflow fields for supplying reactant gases along surfaces of saidelectrodes being formed between said electrolyte electrode assembly andsaid separators, reactant gas passages being connected to said reactantgas flow fields and extending through said fuel cell in the stackingdirection, the fuel cell comprising: a connection channel connectingsaid first reactant gas passage and said first reactant gas flow fieldis provided on said separator; a first reactant gas diffusion layerprovided in said electrolyte electrode assembly; and a second reactantgas diffusion layer provided in said electrolyte electrode assembly,wherein: said separator is a thin metal plate, said connection channelis formed by press forming of said thin metal plate to corrugate saidthin metal plate, a surface area of the first gas diffusion layer islarger than a surface area of the second gas diffusion layer, and thefirst gas diffusion layer of said electrolyte electrode assembly has anoverlapping portion extending on said connection channel such that saidoverlapping portion is tightly attached on said separator for coveringsaid connection channel.
 2. A fuel cell according to claim 1, whereinsaid overlapping portion includes a protruded end protruding from an endof said gas diffusion layer in a direction perpendicular to the stackingdirection.
 3. A fuel cell according to claim 2, wherein at saidprotruded end, a seal member is in contact with a surface opposite to asurface overlapped on said connection channel such that the electrolytemembrane is interposed between said protruded end and said seal member.4. A fuel cell according to claim 2, wherein a plurality of saidprotruded ends are provided symmetrically on said first gas diffusionlayer.
 5. A fuel cell according to claim 1, wherein the first gasdiffusion layer covers the entire surface of the electrolyte membrane.6. A fuel cell according to claim 5, wherein a seal member is disposedon said electrolyte membrane around the second gas diffusion layer.
 7. Afuel cell according to claim 1, wherein said connection channelcomprises a plurality of parallel flow grooves.
 8. A fuel cell accordingto claim 1, wherein the first gas diffusion layer has a hardened portionprovided by adhesive at said first overlapping portion overlapped onsaid connection channel.
 9. A fuel cell according to claim 3, wherein aplurality of said protruded ends are provided symmetrically at saidfirst gas diffusion layer.
 10. A fuel cell according to claim 1,wherein: a plurality of said reactant gas passages extend in a widthdirection from a first end of the separator plate to as second end ofthe separator plate, the plurality of said reactant gas passagesdisposed between a side of the separator plate and the reactant gas flowfield, said overlapping portion having a width extends in the widthdirection of the separator plate, and said overlapping portion coverssaid connection channel such that an entire width of the overlappingportion is smaller than the width of the first reactant gas flow field.11. A fuel cell according to claim 1, wherein the connection channel hasa corrugated shape.